A computer network is a collection of computers linked together so that they can communicate with each other.

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A computer network is a collection of computers
linked together so that they can communicate with
each other. A computer that is not connected to
a network is called a stand-alone computer. There
are two different types of computer
network Local Area Network or LAN - the
computers are all in the same building or in
different buildings on one site permanently
connected to each other with special cables.
Wide Area Network or WAN - the computers are
spread over a large geographical area not
permanently connected to each other communicate
using telephone lines, radio transmitters or
satellite links.
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Local Area Network
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Wide Area Network
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Network security measures are needed to protect
programs and data from the threats that come from
other users and hackers. Data can be kept secure
by giving each network user their own user
identity and password reducing unauthorised
access by allowing users different levels of
access physically restricting access to computer
rooms by locking doors or providing users with
entry codes or special swipe card keys.
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The topology of a network describes the way
cables are used to connect network devices like
servers, workstations or printers. In a bus
topology all the computers are connected through
their own cable to a single central cable - this
is the simplest type of topology.
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In a ring topology computers are connected to
each other forming a large circle. Data is
sent around the ring until it reaches its final
destination. A problem with this topology is
that if one computer fails the entire network
will break down this is one reason why ring
topologies are not used much anymore.
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In a star topology each computer is connected
directly to a central server by a dedicated
cable. This type of topology is very reliable
but the cost of cabling can be quite expensive.
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Advantages of LANs Workstations can share
peripheral devices such as printers. This is
cheaper than buying a printer for every
workstation Workstations dont necessarily need
their own hard disk or CD-ROM drives which makes
them cheaper to buy than stand-alone PCs Users
can save their work centrally on the networks
file server. This means that they can retrieve
their work from any workstation on the network.
They dont need to go back to the same
workstation all the time Users can communicate
with each other and transfer data between
workstations very easily
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One copy of each application package such as a
word processor, spreadsheet etc can be loaded
onto the file server and shared by all users.
When a new version comes out, it only has to be
loaded onto the server instead of onto every
workstation. Disadvantages of LANs Special
security measures are needed to stop users from
using programs and data that they shouldnt have
access to Networks are difficult to set up and
must be maintained by skilled ICT Technicians If
the file server develops a serious fault all the
users are affected, rather than just one user in
the case of a stand-alone machine.